A wireless power transmission system is composed of a power transmitting unit (PTU) for transmitting power in a wireless manner and a power receiving unit (PRU) for receiving power in a wireless manner A PRU receives power by using a resonator including an inductor L and a capacitor C. In this case, an alternating current (AC) having the same frequency as power transmitted by the PTU flows as the power of the resonator. Generally, a final output signal is generated in the form of a stable DC signal and supplied to a load, and thus there is a need for a rectifier. The rectifier converts an AC signal into a direct current (DC) signal that is not regulated. The rectifier converts the signal into a precise DC voltage signal by using a power converter and supplies the DC voltage signal to a load. A PRU has a 2-stage structure regardless of type of a converter used, and power transmission efficiency of the receiving unit is determined by multiplying efficiency of the rectifier and efficiency of the power converter. Accordingly, it is difficult to acquire high efficiency when the power converter has a multi-stage structure.